Since a solar cell is advantageous in that it does not cause pollution, the solar cell is being reevaluated in terms of preservation of global environment. Many researches upon the solar cell as a next-generation clean energy source are being actively conducted.
As such a solar cell, there are currently known several types such as a thin film type solar cell using amorphous silicon, a chemical compound semiconductor solar cell, an organic polymer solar cell, a dye-sensitized solar cell, and so forth. Typically, a solar cell is composed of structures stacked on a base, and the solar cell includes a metal electrode and a photovoltaic conversion layer that collects light and converts the light energy into electric energy. A currently commercialized solar cell using amorphous silicon, however, has not been fully utilized due to high cost for its production and installation.
In 1990s, a dye-sensitized solar cell having low production cost and capable of replacing the amorphous silicon solar cell was reported by Grätzel group in Switzerland. Since then, various researches have been actively conducted to improve photovoltaic conversion efficiency of the dye-sensitized solar cell.
A basic principle of the operation of the dye-sensitized solar cell is as follows. If sun light is incident upon photosensitive dye molecules adsorbed on an n-type metal oxide semiconductor, electrons are excited, and the excited electrons are injected into a conduction band of metal oxide and transferred to transparent conducting oxide electrode. Then, the electrons are transferred again to a counter electrode through an external circuit, whereby electric current becomes of flow. At this time, remaining holes in a photosensitive dye molecule are reduced by an oxidation-reduction electrolyte, during which the oxidized electrolyte component becomes to be reduced by receiving electrons from the counter electrode.
Intensive research efforts have been conducted to improve the photovoltaic conversion efficiency of the solar cell. In this regard, Korean Patent Application Publication No. 2012-0042825 titled “SOLAR CELL AND METHOD FOR FABRICATING THE SAME” discloses a technique for improving efficiency of a solar cell. However, any remarkable achievement in improving efficiency of a solar cell using nanotechnology is yet to be made.